Originally Posted by Nicksta
But, I wonder if the safety compromise is worth it or legal?
Worth it is open for discussion, although as you observed you can see the reason for keeping the shades up while on the ground.
The legal part would depend on the specific airline's Policy and Procedures manual. That, and any later changes to it, describes (among other things) how the airline will meet the requirements of the FAR's. Once approved, the airline is required to operate according to the P&P manual's provisions.
Specific to the shades issue is an FAA requirement to be able to "assess whether opening the emergency exit will increase the hazards to which passengers may be exposed." One airline may propose meeting that requirement by relying on the window in the emergency exit while another may propose meeting the requirement by having all the shades retracted. Once the FAA approves whichever the airline proposes, it is then required.
Asking passengers to close the shades on the ground (usually at the gate) is completely legal as long as the P&P doesn't require the shades to be open. And even if it does have the requirement, it would only apply while passengers are on board since it's a provision for getting the passengers off the airplane in an emergency.